WASHINGTON, D.C.—The blowout of BP’s Macondo well didn’t just spew some 5 million barrels of oil into the Gulf of Mexico last year. Lots of methane also whooshed out, some 500,000 tons in all, according to an estimate[2] published last week. But what happened to the methane is a matter of debate.

Some researchers have concluded[3] in recent papers that almost all of the methane was eaten by an enormous bloom of bacteria. However, microbiologist Samantha Joye of the University of Georgia, Athens, argues that something else happened.

In a presentation[4] here today at the annual meeting of the American Association for the Advancement of Science[5] (which publishes ScienceNOW), Joye described how the breakdown of methane dropped sharply a few months after the blowout began. Methane oxidation by bacteria, which had been 60,000 times higher than normal to the southwest of the well, fell to 300 times above background, according to her unpublished data. Yet there was still plenty of methane in the water.

Joye’s hypothesis is that the microbes ran out of another nutrient, which would have prevented them from metabolizing any more methane. Another factor may explain the decline of methane southwest of the well, Joye said. In late summer her team detected methane to the northeast. “It looks like there’s a significant amount of gas in the ecosystem, but it’s smeared through the ecosystem,” she told the audience.

The fate of the oil and gas released last year is a complicated story, and this finding is unlikely to be the last word. Another expert in the interaction of microbes and hydrocarbons called Joye’s “surprising” and declined to comment until a peer-reviewed paper is published.